Method and pretreatment method for transferring two-dimensional film from mica substrate

Abstract

The present invention belongs to the technical field of film transfer, and particularly relates to a method and pretreatment method for transferring a two-dimensional film from a mica substrate. The present invention successively treats a mica substrate with an acidic solution and an alkali metal chloride solution, which can weaken the binding force of the mica substrate to a two-dimensional film without damaging the two-dimensional film, thereby significantly improving the transfer quality of the two-dimensional film, reducing material defects and lattice distortion introduced by the transfer, and achieving the purpose of conveniently and efficiently transferring a high-quality two-dimensional film. The pretreatment method provided by the present disclosure is applicable to transfer processes of different types of two-dimensional films, and has high transfer success rate, less sample damage, low cost and high efficiency.

Description

A method for transferring two-dimensional thin films from a mica substrate and a pretreatment method Technical Field

[0001] This invention belongs to the field of thin film transfer technology, specifically relating to a method for transferring two-dimensional thin films from a mica substrate and a pretreatment method. Background Technology

[0002] With the advancement of materials growth and synthesis technologies, two-dimensional thin film materials have broad application prospects and significant importance in scientific research and industrial production due to their excellent electrical conductivity, thermal conductivity, mechanical toughness, and catalytic properties.

[0003] Before discussing the performance of devices containing two-dimensional thin-film materials, a key issue is how to transfer high-quality two-dimensional thin films to the target substrate. During the synthesis of two-dimensional thin films, the mica substrate surface contains numerous dangling bonds. The two-dimensional thin film bonds with some of these dangling bonds, resulting in extremely strong adhesion between the mica substrate and the two-dimensional thin film, significantly increasing the difficulty of the transfer process. The adhesion force between the adhesive layer material and the two-dimensional thin film in traditional wet and dry transfer techniques is far less than the adhesion force between the mica substrate and the two-dimensional thin film. This leads to damage to the two-dimensional thin film during the transfer process due to excessive underlying adhesion forces, severely limiting the quality of the two-dimensional thin film. Summary of the Invention

[0004] The purpose of this invention is to provide a method for transferring two-dimensional thin films from a mica substrate and a pretreatment method. The pretreatment method provided by this invention can reduce the bonding force between the two-dimensional thin film and the mica substrate, and significantly improve the quality of two-dimensional thin film transfer.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a pretreatment method for transferring two-dimensional thin films from a mica substrate, comprising:

[0007] The mica substrate on which the two-dimensional thin film is grown is first impregnated in an acidic solution, and then impregnated in an alkali metal chloride solution; the acidic solution does not react with the two-dimensional thin film.

[0008] Preferably, the acidic solution includes a hydrofluoric acid solution or a hydrochloric acid solution; the mass concentration of the acidic solution is 0.5% to 2%.

[0009] Preferably, the first immersion temperature is room temperature and the time is 1 to 3 minutes.

[0010] Preferably, the alkali metal chloride solution includes a sodium chloride solution or a potassium chloride solution; the concentration of the alkali metal chloride solution is 0.5–2 mol / L.

[0011] Preferably, the second impregnation is performed under heating and ultrasonic conditions; the heating temperature is 50-70°C, the ultrasonic power is 40-60W, and the time is 3-5 minutes.

[0012] Preferably, the two-dimensional thin film includes a Bi2O2Se thin film, a Bi2Se3 thin film, a MoS2 thin film, or a WSe2 thin film.

[0013] The present invention also provides a method for transferring a two-dimensional thin film from a mica substrate, comprising the following steps:

[0014] The preprocessing method described above is used to preprocess the mica substrate to obtain the preprocessed mica substrate.

[0015] A polymer solution is coated on the side of the treated mica substrate where a two-dimensional film has grown, to obtain a mica substrate with a polymer layer.

[0016] The mica substrate with the polymer layer was placed in water and peeled off to obtain a polymer layer carrying a two-dimensional film.

[0017] After removing impurities from the polymer layer carrying the two-dimensional film, it is attached to the surface of the target substrate so that the side carrying the two-dimensional film is in contact with the target substrate. After removing the polymer layer, the transfer of the two-dimensional film is completed.

[0018] Preferably, the polymer solution comprises a polypropylene carbonate solution and a polymethyl methacrylate solution.

[0019] Preferably, the impurity removal method involves immersing the polymer carrying the two-dimensional film in an inorganic alkaline solution; the inorganic alkaline solution includes a sodium hydroxide solution or a potassium hydroxide solution; and the concentration of the inorganic alkaline solution is 0.5–2 mol / L.

[0020] Preferably, the method for removing the polymer layer is to dissolve it using an organic solvent, which includes one or more of acetone, isopropanol, and toluene.

[0021] The present invention provides a pretreatment method for transferring a two-dimensional thin film from a mica substrate, comprising: first impregnating the mica substrate on which the two-dimensional thin film is grown in an acidic solution, and then impregnating it in an alkali metal chloride solution; wherein the acidic solution does not react with the two-dimensional thin film.

[0022] This invention utilizes acidic and alkali metal chloride solutions to treat the mica substrate sequentially. This weakens the adhesion between the mica substrate and the two-dimensional thin film without damaging the film, significantly improving the quality of two-dimensional film transfer. It also reduces material defects and lattice distortion introduced during transfer, achieving convenient and efficient transfer of high-quality two-dimensional thin films. The pretreatment method provided by this invention is applicable to transfer processes of different types of two-dimensional thin films, and features high transfer success rate, minimal sample damage, low cost, and high efficiency. Attached Figure Description

[0023] Figure 1 is a schematic flowchart of the transfer method provided by the present invention;

[0024] Figure 2 shows physical images of Bi2O2Se thin films transferred using the conventional transfer method and the transfer methods provided in Examples 1-3;

[0025] Figure 3 shows a comparison of the photocurrent response and device noise of Bi2O2Se thin films obtained using the conventional transfer method and the transfer methods provided in Examples 1-3. Detailed Implementation

[0026] This invention provides a pretreatment method for transferring two-dimensional thin films from a mica substrate, comprising:

[0027] The mica substrate on which the two-dimensional thin film is grown is first impregnated in an acidic solution, and then impregnated in an alkali metal chloride solution; the acidic solution does not react with the two-dimensional thin film.

[0028] In this invention, the two-dimensional thin film preferably includes a Bi₂O₂Se thin film, a Bi₂Se₃ thin film, a MoS₂ thin film, or a WSe₂ thin film. In this invention, the mica substrate preferably has a size of 1*1 cm and a thickness of 200 μm. In this invention, the two-dimensional thin film preferably has a size of 50*50 μm and a thickness of 10 nm.

[0029] In this invention, the acidic solution includes a hydrofluoric acid solution or a hydrochloric acid solution; the mass concentration of the acidic solution is 0.5% to 2%, specifically 0.5%, 1%, 1.5%, or 2%. In this invention, when the two-dimensional thin film is a Bi₂O₂Se thin film, the acidic solution is preferably a hydrofluoric acid solution. In this invention, the temperature of the first impregnation is preferably room temperature, and the time is preferably 1 to 3 minutes. After the first impregnation, this invention further preferably includes cleaning the impregnated substrate with deionized water and then drying it with a nitrogen gun for later use.

[0030] In this invention, because the acidic solution has a corrosive effect on the mica substrate but no corrosive effect on the two-dimensional film, the dangling molecular bonds on the surface of the mica substrate are broken, making it easier for the two-dimensional film to be peeled off from the mica substrate.

[0031] In this invention, the alkali metal chloride solution preferably includes a sodium chloride solution or a potassium chloride solution; the concentration of the alkali metal chloride solution is preferably 0.5–2 mol / L, specifically 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L. In this invention, the second impregnation is preferably carried out under heating and ultrasonic conditions; the heating temperature is preferably 50–70°C, specifically 50°C, 60°C, or 70°C; the ultrasonic power is preferably 40–60 W, specifically 40 W, 50 W, or 60 W; and the time is preferably 3–5 min. After the second impregnation, this invention further preferably includes drying the impregnated mica substrate with a nitrogen gun for later use. In this invention, the Cl in the alkali metal chloride solution... - Ions and alkali metal cations can combine with unpaired dangling bonds on the mica substrate surface due to lattice termination, forming stable chemical bonds. This process neutralizes the unpaired electrons of the dangling bonds, reducing the adhesion between the mica substrate and the organic film. Simultaneously, because the two-dimensional film material surface lacks dangling bonds, it is less likely to combine with ions from the alkali metal chloride solution, allowing for strong contact with the organic film and further promoting the separation of the two-dimensional film from the mica substrate. Simultaneously, an alkali metal chloride crystalline film forms on the surface of the mica substrate in areas where no two-dimensional film has grown. In this invention, the alkali metal chloride crystalline film protects the mica substrate surface, preventing dissociation during transfer due to the strong adsorption of the organic film; simultaneously, the alkali metal chloride crystalline film also increases the hydrophilicity of the mica surface, improving the peeling efficiency.

[0032] The present invention also provides a method for transferring a two-dimensional thin film from a mica substrate, comprising the following steps:

[0033] The preprocessing method described above is used to preprocess the mica substrate to obtain the preprocessed mica substrate.

[0034] A polymer solution is coated on the side of the treated mica substrate where a two-dimensional film has grown, to obtain a mica substrate with a polymer layer.

[0035] The mica substrate with the polymer layer was placed in water and peeled off to obtain a polymer layer carrying a two-dimensional film.

[0036] The polymer layer carrying the two-dimensional film is immersed in an inorganic alkaline solution and then attached to the surface of the target substrate. The transfer of the two-dimensional film is completed after the polymer layer is removed.

[0037] This invention employs the preprocessing method described in the above technical solution to obtain a processed mica substrate. In this invention, the preprocessing procedure preferably refers to the steps of the preprocessing method described in the above technical solution, and will not be repeated here.

[0038] After obtaining the treated mica substrate, the present invention coats a polymer solution onto the side of the treated mica substrate on which a two-dimensional thin film is grown, thereby obtaining a mica substrate with a polymer layer.

[0039] In this invention, the polymer solution preferably comprises polymethyl methacrylate (PMMA) solution and polypropylene carbonate (PPC) solution.

[0040] In this invention, the coating polymer solution is preferably coated sequentially with a polymethyl methacrylate solution and a polypropylene carbonate solution. In this invention, the coating method is preferably spin-coating.

[0041] In this invention, the preferred method for coating with polymethyl methacrylate (PMMA) solution is as follows: PMMA solution is dropwise added to the side of the treated mica substrate on which the two-dimensional film is grown; the substrate is then spin-coated at 500 rpm for 5 seconds, followed by spin-coating at 3000 rpm for 30 seconds. After spin-coating, the substrate is placed on a hot plate at 150°C and baked for 5 minutes to obtain a PMMA layer. In this invention, the mass concentration of the PMMA solution is preferably 6-10%, and the solvent is preferably anisole. In this invention, the thickness of the PMMA layer is preferably 400 nm, and the size of the PMMA layer is preferably the same as the size of the mica substrate.

[0042] In this invention, the preferred process for coating with the polypropylene carbonate solution is as follows: The polypropylene carbonate solution is drop-coated onto the surface of the polymethyl methacrylate layer, first spin-coated at 500 rpm for 5 seconds, then spin-coated at 3000 rpm for 30 seconds. After spin-coating, the layer is placed on a hot plate at 120°C and baked for 3 minutes to form the polypropylene carbonate layer. In this invention, the preferred mass concentration of the polypropylene carbonate solution is 15%, and the preferred solvent is anisole. In this invention, the preferred thickness of the polypropylene carbonate layer is 600 nm, and the preferred dimensions of the polypropylene carbonate layer are the same as the dimensions of the mica substrate.

[0043] After obtaining the mica substrate with the polymer layer, the present invention places the mica substrate with the polymer layer in water for peeling to obtain a polymer layer carrying a two-dimensional film.

[0044] In this invention, the water is preferably deionized water, and the peeling time is preferably 30 minutes. After peeling, the invention further preferably includes using tweezers to peel the polymer layer carrying the two-dimensional film from the surface of the mica substrate. In this invention, due to the surface tension of the material, the polymer layer carrying the two-dimensional film will lie flatly on the surface of the deionized water.

[0045] After obtaining the polymer layer carrying the two-dimensional film, the present invention removes impurities from the polymer layer carrying the two-dimensional film and attaches it to the surface of the target substrate, so that the side carrying the two-dimensional film is in contact with the target substrate. After removing the polymer layer, the transfer of the two-dimensional film is completed.

[0046] In this invention, the preferred method for impurity removal is to immerse the polymer layer carrying the two-dimensional film in an inorganic alkaline solution; the inorganic alkaline solution preferably includes a sodium hydroxide solution or a potassium hydroxide solution; the concentration of the inorganic alkaline solution is preferably 0.5–2 mol / L, specifically 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L. In this invention, by immersing in the inorganic alkaline solution, due to the high solubility of alkali metal chloride crystals, the alkali metal chlorides on the surface of the polymer layer dissolve in the solution; mica fragments react with the inorganic alkaline solution and dissolve in the solution, thereby removing the alkali metal chlorides and mica fragments from the polymer layer, achieving impurity removal.

[0047] This invention does not have any particular limitation on the type of target substrate; any substrate well known to those skilled in the art can be used. In this invention, the attachment process is preferably as follows: the polymer layer carrying the two-dimensional film, after being impregnated, is spread flat on the surface of deionized water, with the side carrying the two-dimensional film facing upwards. The target substrate is held with tweezers, and the target substrate is slowly moved close to the polymer layer carrying the two-dimensional film on the surface of the deionized water until the two-dimensional film is completely adhered to the surface of the target substrate.

[0048] In this invention, the method for removing the polymer layer preferably involves dissolving it with an organic solvent, which preferably includes one or more of acetone, isopropanol, and toluene; the acetone is preferably anhydrous acetone. This invention does not have a specific limitation on the dissolution time, as long as the polymer layer is completely dissolved. After dissolution, this invention further preferably includes drying the target substrate with nitrogen gas to complete the transfer.

[0049] Figure 1 shows a schematic diagram of the transfer method provided by the present invention.

[0050] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0051] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0052] Example 1

[0053] Step 1: Prepare hydrogen fluoride solution: Take 5g of 15% industrial hydrogen fluoride solution into a polyethylene (PP) bottle containing 70g of deionized water, and shake thoroughly to ensure that the industrial hydrogen fluoride solution and deionized water are completely mixed to obtain a 1% hydrogen fluoride solution.

[0054] Step 2: Prepare sodium chloride solution: Take 2.925g of sodium chloride crystals into a polyethylene (PP) bottle containing 50mL of deionized water, shake thoroughly to ensure complete dissolution of the sodium chloride crystals, and obtain a sodium chloride solution with a molar concentration of 1mol / L.

[0055] Step 3: Prepare PPC solution: Dissolve 3g of PPC in 17g of anisole, place on a magnetic stirrer and stir at 90℃ for 2h to obtain PPC solution; PMMA solution is industrial grade A5 PMMA, and its ratio is 6% PMMA / anisole solution by mass.

[0056] Step 4: Prepare sodium hydroxide solution. Take 2g of sodium hydroxide into a polyethylene (PP) bottle containing 50mL of deionized water, shake thoroughly to ensure complete dissolution of the sodium hydroxide, and obtain a sodium hydroxide solution with a molar concentration of 1mol / L;

[0057] Step 5: Place the mica substrate with Bi2O2Se film grown by CVD into a 1% hydrogen fluoride solution and let it stand at room temperature for 3 minutes. Then take it out, wash it with deionized water, and dry it with a nitrogen gun for later use.

[0058] Step 6: Place the mica substrate obtained in Step 5 into a 1 mol / L sodium chloride solution, heat it in a water bath at 60°C while sonicating it at 50W for 5 minutes, then remove the mica substrate from the sodium chloride solution and dry it with a nitrogen gun for later use to obtain the treated mica substrate.

[0059] Step 7: Place the processed mica substrate on the rotating vacuum stage of the spin coater, vacuum adsorb the mica substrate, drop PMMA solution onto the surface, spin coat at 500 rpm for 5 s, then spin coat at 3000 rpm for 30 s, remove the mica substrate and bake it on a hot plate at 150℃ for 5 min to obtain a PMMA layer with a thickness of 400 nm; place the mica substrate on the rotating vacuum stage of the spin coater again, vacuum adsorb the mica substrate, drop PPC solution onto the surface of the PMMA layer, spin coat at 500 rpm for 5 s, then spin coat at 3000 rpm for 30 s, remove the mica substrate and bake it on a hot plate at 120℃ for 3 min to complete the preparation of the PMMA / PPC polymer layer;

[0060] Step 8: Place the mica substrate obtained in Step 7 into deionized water and soak for 30 minutes. Then, use tweezers to peel the PMMA / PPC polymer layer carrying the Bi2O2Se film from the mica surface from the edge of the mica substrate. The resulting PMMA / PPC polymer layer carrying the Bi2O2Se film is flatly spread on the surface of the deionized water.

[0061] Step 9: Spread the PMMA / PPC polymer layer carrying the Bi2O2Se film obtained in Step 8 flatly on the surface of a 1mol / L sodium hydroxide solution and remove the sodium chloride crystals and mica fragments on it.

[0062] Step 10: Spread the PMMA / PPC polymer layer treated in Step 9 flat on the surface of deionized water. Hold the target substrate with tweezers and slowly bring the target substrate close to the Bi2O2Se film on the surface of deionized water until the Bi2O2Se film is completely adhered to the surface of the target substrate.

[0063] Step 11: Place the target substrate obtained in Step 10 into a glass container, add acetone and soak for 10 minutes. The PMMA / PPC polymer layer will be dissolved, and the Bi2O2Se film will adhere to the target substrate. After gently drying with a nitrogen gun, the transfer is complete.

[0064] Example 2

[0065] Step 1: Prepare hydrogen fluoride solution: Take 5g of 15% industrial hydrogen fluoride solution into a polyethylene (PP) bottle containing 145g of deionized water, and shake thoroughly to ensure complete mixing of the industrial hydrogen fluoride solution and deionized water, to obtain a 0.5% hydrogen fluoride solution.

[0066] Step 2: Prepare sodium chloride solution: Take 2.925g of sodium chloride crystals into a polyethylene (PP) bottle containing 100mL of deionized water, shake thoroughly to ensure complete dissolution of the sodium chloride crystals, and obtain a sodium chloride solution with a molar concentration of 0.5mol / L.

[0067] Step 3: Prepare PPC solution: Dissolve 3g of PPC in 17g of anisole, place on a magnetic stirrer and stir at 90℃ for 2h to obtain PPC solution; PMMA solution is industrial grade A5 PMMA, and its ratio is 6% PMMA / anisole solution by mass.

[0068] Step 4: Prepare sodium hydroxide solution. Take 2g of sodium hydroxide into a polyethylene (PP) bottle containing 100mL of deionized water, shake thoroughly to ensure complete dissolution of the sodium hydroxide, and obtain a sodium hydroxide solution with a molar concentration of 0.5mol / L;

[0069] Step 5: Place the mica substrate with Bi2O2Se film grown by CVD into a 0.5% hydrogen fluoride solution and let it stand at room temperature for 3 minutes. Then take it out, wash it with deionized water, and dry it with a nitrogen gun for later use.

[0070] Step 6: Place the mica substrate obtained in Step 5 into a 0.5 mol / L sodium chloride solution, heat it in a water bath at 50°C while sonicating it at 40W for 5 minutes, then remove the mica substrate from the sodium chloride solution and dry it with a nitrogen gun for later use to obtain the treated mica substrate.

[0071] Step 7: Place the processed mica substrate on the rotating vacuum stage of the spin coater, vacuum adsorb the mica substrate, drop PMMA solution onto the surface, spin coat at 500 rpm for 5 s, then spin coat at 3000 rpm for 30 s, remove the mica substrate and bake it on a hot plate at 150℃ for 5 min to obtain a PMMA layer with a thickness of 400 nm; place the mica substrate on the rotating vacuum stage of the spin coater again, vacuum adsorb the mica substrate, drop PPC solution onto the surface of the PMMA layer, spin coat at 500 rpm for 5 s, then spin coat at 3000 rpm for 30 s, remove the mica substrate and bake it on a hot plate at 120℃ for 3 min to complete the preparation of the PMMA / PPC polymer layer;

[0072] Step 8: Place the mica substrate obtained in Step 7 into deionized water and soak for 30 minutes. Then, use tweezers to peel the PMMA / PPC polymer layer carrying the Bi2O2Se film from the mica surface from the edge of the mica substrate. The resulting PMMA / PPC polymer layer carrying the Bi2O2Se film is flatly spread on the surface of the deionized water.

[0073] Step 9: Spread the PMMA / PPC polymer layer carrying the Bi2O2Se film obtained in Step 8 flatly on the surface of a 0.5 mol / L sodium hydroxide solution and remove the sodium chloride crystals and mica fragments on it.

[0074] Step 10: Spread the PMMA / PPC polymer layer treated in Step 9 flat on the surface of deionized water. Hold the target substrate with tweezers and slowly bring the target substrate close to the Bi2O2Se film on the surface of deionized water until the Bi2O2Se film is completely adhered to the surface of the target substrate.

[0075] Step 11: Place the target substrate obtained in Step 10 into a glass container, add acetone and soak for 10 minutes. The PMMA / PPC polymer layer will be dissolved, and the Bi2O2Se film will adhere to the target substrate. After gently drying with a nitrogen gun, the transfer is complete.

[0076] Example 3

[0077] Step 1: Prepare hydrogen fluoride solution: Take 5g of 15% industrial hydrogen fluoride solution into a polyethylene (PP) bottle containing 32.5g of deionized water, and shake thoroughly to ensure complete mixing of the industrial hydrogen fluoride solution and deionized water, to obtain a 2% hydrogen fluoride solution.

[0078] Step 2: Prepare sodium chloride solution: Take 2.925g of sodium chloride crystals into a polyethylene (PP) bottle containing 25mL of deionized water, shake thoroughly to ensure complete dissolution of the sodium chloride crystals, and obtain a sodium chloride solution with a molar concentration of 2mol / L.

[0079] Step 3: Prepare PPC solution: Dissolve 3g of PPC in 17g of anisole, place on a magnetic stirrer and stir at 90℃ for 2h to obtain PPC solution; PMMA solution is industrial grade A5 PMMA, and its ratio is 6% PMMA / anisole solution by mass.

[0080] Step 4: Prepare sodium hydroxide solution. Take 2g of sodium hydroxide into a polyethylene (PP) bottle containing 25mL of deionized water, and shake thoroughly to ensure complete dissolution of the sodium hydroxide, obtaining a sodium hydroxide solution with a molar concentration of 2mol / L;

[0081] Step 5: Place the mica substrate with Bi2O2Se film grown by CVD into a 2% hydrogen fluoride solution and let it stand at room temperature for 3 minutes. Then take it out, wash it with deionized water, and dry it with a nitrogen gun for later use.

[0082] Step 6: Place the mica substrate obtained in Step 5 into a 2 mol / L sodium chloride solution, heat it in a water bath at 70°C while sonicating it at 60W for 5 minutes, then remove the mica substrate from the sodium chloride solution and dry it with a nitrogen gun for later use to obtain the treated mica substrate.

[0083] Step 7: Place the processed mica substrate on the rotating vacuum stage of the spin coater, vacuum adsorb the mica substrate, drop PMMA solution onto the surface, spin coat at 500 rpm for 5 s, then spin coat at 3000 rpm for 30 s, remove the mica substrate and bake it on a hot plate at 150℃ for 5 min to obtain a PMMA layer with a thickness of 400 nm; place the mica substrate on the rotating vacuum stage of the spin coater again, vacuum adsorb the mica substrate, drop PPC solution onto the surface of the PMMA layer, spin coat at 500 rpm for 5 s, then spin coat at 3000 rpm for 30 s, remove the mica substrate and bake it on a hot plate at 120℃ for 3 min to complete the preparation of the PMMA / PPC polymer layer;

[0084] Step 8: Place the mica substrate obtained in Step 7 into deionized water and soak for 30 minutes. Then, use tweezers to peel the PMMA / PPC polymer layer carrying the Bi2O2Se film from the mica surface from the edge of the mica substrate. The resulting PMMA / PPC polymer layer carrying the Bi2O2Se film is flatly spread on the surface of the deionized water.

[0085] Step 9: Spread the PMMA / PPC polymer layer carrying the Bi2O2Se film obtained in Step 8 flatly on the surface of a 2mol / L sodium hydroxide solution and remove the sodium chloride crystals and mica fragments on it.

[0086] Step 10: Spread the PMMA / PPC polymer layer treated in Step 9 flat on the surface of deionized water. Hold the target substrate with tweezers and slowly bring the target substrate close to the Bi2O2Se film on the surface of deionized water until the Bi2O2Se film is completely adhered to the surface of the target substrate.

[0087] Step 11: Place the target substrate obtained in Step 10 into a glass container, add acetone and soak for 10 minutes. The PMMA / PPC polymer layer will be dissolved, and the Bi2O2Se film will adhere to the target substrate. After gently drying with a nitrogen gun, the transfer is complete.

[0088] Performance testing

[0089] Test Example 1

[0090] Figure 2 shows physical images of Bi2O2Se films obtained by the traditional thin film transfer method (i.e., the transfer method without pretreatment steps) and the transfer methods of Examples 1 to 3. In Figure 2(1), the Bi2O2Se film obtained by the traditional thin film transfer method is shown; in Figure 2(2), the Bi2O2Se film obtained by Example 1 is shown; in Figure 2(3), the Bi2O2Se film obtained by Example 2 is shown; and in Figure 2(4), the Bi2O2Se film obtained by Example 3 is shown. It can be seen that the transfer method provided by the present invention can significantly reduce the bonding force of the mica surface to the target Bi2O2Se film, greatly improve the transfer efficiency, and avoid the damage of the film material during the transfer process.

[0091] Figure 3 shows a comparison of the photocurrent response of Bi2O2Se thin films obtained by the conventional thin film transfer method without pretreatment and the transfer methods of Examples 1 to 3 (Figure 3(1)) and a comparison of device noise (Figure 3(2)).

[0092] Photocurrent testing method: The thin-film device was irradiated with a THORLABS PL520 laser with a power of 5 microwatts, and the photocurrent value of the device was recorded using a Keithley 2400 source meter.

[0093] Noise current testing method: Under dark conditions, record the device noise current value using a DSA800 spectrum analyzer. The detectivity is calculated using the following formula: Where A is the photosensitive area of ​​the device, which is 2.5 × 10⁻⁶ in this experiment. -5 cm 2 R is the device responsivity (unit: A / W), defined as the ratio of photocurrent to incident light power. n This refers to device noise.

[0094] In Figure 3(1), the black curve represents the photocurrent response of the device using the Bi2O2Se thin film obtained in Example 1, the red curve represents the photocurrent response of the device using the Bi2O2Se thin film obtained in Example 2, the blue curve represents the photocurrent response of the device using the Bi2O2Se thin film obtained in Example 3, and the purple line represents the photocurrent response of the device using the Bi2O2Se thin film obtained using the conventional transfer method. In Figure 3(2), the green dotted line represents the noise current level of the device using the Bi2O2Se thin film obtained in Example 1, the purple dotted line represents the noise current level of the device using the Bi2O2Se thin film obtained in Example 2, the red dotted line represents the noise current level of the device using the Bi2O2Se thin film obtained in Example 3, and the blue dotted line represents the noise current level of the device using the Bi2O2Se thin film obtained using the conventional transfer method; the specific test results are shown in Table 1.

[0095] Table 1 shows the performance test results of the thin film devices obtained using the examples.

[0096] It can be seen that the transfer method provided by the present invention can significantly improve the film quality of the target Bi2O2Se film, improve the photoresponse capability of the device using the Bi2O2Se film, and reduce noise caused by factors such as carrier generation and recombination.

[0097] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A pretreatment method for transferring two-dimensional thin films from a mica substrate, characterized in that, include: The mica substrate with the two-dimensional thin film grown on it is first impregnated in an acidic solution, and then impregnated in an alkali metal chloride solution. The acidic solution does not react with the two-dimensional thin film.

2. The pretreatment method according to claim 1, characterized in that, The acidic solution includes hydrofluoric acid solution or hydrochloric acid solution; the mass concentration of the acidic solution is 0.5% to 2%.

3. The pretreatment method according to claim 1 or 2, characterized in that, The first immersion temperature is room temperature, and the time is 1 to 3 minutes.

4. The pretreatment method according to claim 1, characterized in that, The alkali metal chloride solution includes a sodium chloride solution or a potassium chloride solution; the concentration of the alkali metal chloride solution is 0.5–2 mol / L.

5. The pretreatment method according to claim 1 or 4, characterized in that, The second impregnation is carried out under heating and ultrasonic conditions; the heating temperature is 50-70°C, the ultrasonic power is 40-60W, and the time is 3-5 minutes.

6. The pretreatment method according to claim 1, characterized in that, The two-dimensional thin film includes Bi2O2Se thin film, Bi2Se3 thin film, MoS2 thin film or WSe2 thin film.

7. A method for transferring a two-dimensional thin film from a mica substrate, characterized in that, Includes the following steps: The preprocessing method described in any one of claims 1 to 6 is used to perform preprocessing to obtain the processed mica substrate; A polymer solution is coated on the side of the treated mica substrate where a two-dimensional film has grown, to obtain a mica substrate with a polymer layer. The mica substrate with the polymer layer was placed in water and peeled off to obtain a polymer layer carrying a two-dimensional film. After removing impurities from the polymer layer carrying the two-dimensional film, it is attached to the surface of the target substrate so that the side carrying the two-dimensional film is in contact with the target substrate. After removing the polymer layer, the transfer of the two-dimensional film is completed.

8. The method according to claim 7, characterized in that, The polymer solution includes a polypropylene carbonate solution and a polymethyl methacrylate solution.

9. The method according to claim 7, characterized in that, The method of removing impurities involves immersing the polymer layer carrying the two-dimensional film in an inorganic alkaline solution; the inorganic alkaline solution includes sodium hydroxide solution or potassium hydroxide solution; the concentration of the inorganic alkaline solution is 0.5 to 2 mol / L.

10. The method according to claim 7, characterized in that, The method for removing the polymer layer is to dissolve it using an organic solvent, which includes one or more of acetone, isopropanol, and toluene.

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